Molar mass is the sum of the masses of all the atoms found in one mole of a substance. It is measured in grams per mole. Molar mass is depicted for elements or molecules. In the case of single elements or individual atoms, the molar mass is simply the element’s mass expressed in atomic mass units.
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Definition: The elemental symbol for iron is Fe, and the molecular mass is 55.845 to three decimal places, according to the periodic table. |
What is the Molar Mass of Iron Chemistry Questions with Solutions
Q-1: Molar mass of iron is the _________.
a) Mass of one atom of Fe
b) Mass of 1 mole of Fe
c) Both a) and b)
d) Can’t be predicted
Answer: b) Mass of 1 mole of Fe.
Q-2: 9.7×1017 atoms of iron weigh as much as 1 cc of H2 at STP. What is the atomic mass of iron?
Answer: Mass of 1 cc of H2 at S.T.P = 2.016/22400 = 9.0 × 10-5 g
Thus, 9.7×1017 atoms of iron have mass = 9.0 × 10-5 g
Therefore, mass of one mole, that is, 6.022 × 1023 atoms of Fe = (9.0 × 10-5 × 6.022 × 1023)/(9.7×1017) = 55.9 g
Q-3: What is the mass of iron present in 0.5 mole of K4[Fe(CN)6]?
Answer: 1 mol of K4[Fe(CN)6] contains Fe= 1 g atom
0.5 mol of K4[Fe(CN)6] contains Fe = 1× 0.5 g atom = 0.5 g atom = 0.5 × 56 g = 28 g
Q-4: Which of the following will contain the greater moles of atoms?
a) 0.8 g of iron
b) 1 g of iron
c) 50 g of iron
Answer: c) 50 g of iron
Molar mass of iron = 56g/mol
Number of moles = Given weight/Molar mass
a) Number of moles of iron = 0.8/56 = 0.0143 moles
It means 0.8 g of iron contains 0.0143 moles of atoms.
b) Number of moles of iron = 1/56 = 0.0178 moles
It means 1 g of iron contains 0.0178 moles of atoms.
c) Number of moles of iron = 50/56 = 0.9 moles
It means 50 g of iron contains 0.9 moles of atoms.
Hence, 50 g of iron contains the greater moles of atoms.
Q-5: Gram atomic mass of iron is equal to ______.
a) One mole of iron
b) 6.022×1023 atoms of iron
c) One gram atom of iron
d) All of the above
Answer: d) All of the above
Explanation: Gram atomic mass of an element may be defined as the mass of Avogadro’s number of atoms, i.e. 6.022×1023 atoms.
In the case of atomic substances,1 mole = gram atomic mass or 1 g atom of the element = 6.022×1023 atoms of the element.
Q-6: What is the distinction between a mass of a molecule and gram molecular mass?
Answer: The mass of a molecule is the actual mass of a single molecule expressed in grams, whereas gram molecular mass is the mass in grams of Avogadro’s number of molecules.
Q-7: Calculate the molar mass of iron(III) bromide hexahydrate, a catalyst in organic reactions.
a) 355.5 g/mol
b) 403.5 g/mol
c) 317.6 g/mol
d) 295.6 g/mol
Answer: b) 403.5 g/mol
Explanation: The chemical formula for iron(III) bromide hexahydrate is [Fe(H2O)6]Br3.
Molar mass of [Fe(H2O)6]Br3 = Molar mass of Fe + 6(Molecular mass of H2O) + 3(Molar mass of Br)
Molar mass of [Fe(H2O)6]Br3 =55.8+6(18)+3(79.9)
= 403.5 g/mol
Q-8: Determine how many moles of Fe are present in a sample of 200 grams of pure Fe using the molar mass of Fe.
Answer: Molar mass of Fe = 56 g/mol
Number of moles = Weight of Fe/ Molar mass of Fe
= (200 g)/ (56 g/mol)
= 3.6 mol
Q-9:The molar mass of iron divided by its density at the given temperature and pressure yields its _______.
a) Molar density
b) Molar volume
c) Mole fraction
d) Molar weight
Answer: b) Molar volume.
Q-10: Using the molar mass of iron, how can you calculate the equivalent mass of Fe in iron(III) nitrate, Fe(NO3)2?
Answer: Equivalent mass of Fe = Molar mass of Fe/Valency of the Fe
In Fe(NO3)2, Fe has a valency(charge) of 2.
Molar mass of Fe = 56 u
Equivalent mass of Fe = 56/2 = 28
Q-11: Why does iron have a larger molar mass than sulphur? (Mass number of iron = 56 and mass number of sulphur is 32)
Answer: Because iron has 30 neutrons and 26 protons, it has a higher molar mass. Sulphur has 16 protons and 16 neutrons, while neutrons and protons have similar masses. Because sulphur contains fewer protons and neutrons than iron, its molar mass is lower.
Q-12: Why is the atomic mass of Fe an average value?
Answer: Fe exists in different isotopes, that is, atoms with different masses; for example, Fe exists in three isotopes with mass numbers 54, 56 and 57. Atomic mass is the sum of the products of fractional abundances of the isotopes of Fe and the corresponding mass numbers. As a result, the atomic mass of iron comes out to be an average value.
Q-13: What will be the mass of one atom of Fe in grams?
Answer: 1 mol of Fe atoms = 56 g = 6.022 × 1023 atoms
Thus, 6.022 × 1023 atoms of Fe have mass = 56 g
Therefore, 1 atom of Fe will have mass = 56/(6.022 × 1023) g= 9.299 × 10-23 g
Q-14: Write the chemical formula for the following and then calculate the molar mass:
a) Green vitriol
b) Ferrous nitrate
Answer:
a) The chemical formula for green vitriol is FeSO4.7H2O.
Molar mass of FeSO4.7H2O= 56+32+4(16) +7(18) = 278 u
b) The chemical formula for ferric nitrate is Fe(NO3)3.
Molar mass of Fe(NO3)3 = 56+ 3(14+16(3)) = 242 g
Q-15: Determine the empirical formula for an iron oxide with 69.9% Fe and 30.1% oxygen by mass. (Molar mass: Fe= 55.85 amu, O = 16 amu)
Answer:
|
Element |
Symbol |
% by Mass |
Atomic Mass |
Moles of the Element |
Simplest Molar Ratio |
Simplest Whole Number Molar Ratio |
|---|---|---|---|---|---|---|
|
Iron |
Fe |
69.9 |
55.85 |
69.9/55.85 = 1.25 |
1.25/1.25 = 1 |
2 |
|
Oxygen |
O |
30.1 |
16.00 |
30.1/16.00 = 1.88 |
1.88/1.25 =1.5 |
3 |
Therefore, the empirical formula is Fe2O3.
Practice Questions on What is the Molar Mass of Iron
Q-1: Calculate the iron, sulphur, and oxygen mass percentages in ferric sulphate, a compound used in water and sewage treatment to aid in the removal of suspended impurities.
(Molar mass of Fe: 56 g/mol, S = 32 g/mol, O= 16 g/mol)
Q-2: Mass of 1 mole of Fe is known as its ______.
a) Gram Atomic mass
b) Gram molecular mass
c) Molar mass
d) Molecular mass
Q-3: Molar mass of iron atom can be obtained by multiplying Avogadro’s number to _____.
a) Mass of 1 mole Fe atom
b) Mass of single Fe atom
c) Mass of one gram Fe-atom
d) Given mass of Fe
Q-4: In the balanced equation,
3Fe + 4H2O → Fe3O4+ 4H2
a) Calculate the molar mass of Fe3O4.
b) Calculate the mass of Fe, which will be converted into its oxide by the action of 36 g of steam on it.
Q-5: What is the difference between the 6.5 × 103 g of Fe and 6.50 × 103 g of Fe?
Click the PDF to check the answers for Practice Questions.
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